1. Field of the Invention
The present invention relates generally to a system and method for offering communication technology, and in particular, to a system and method for offering different communication technologies.
2. Description of the Related Art
Generally, next generation wireless communication systems are expected to provide a multimedia service, which has already been provided in a 3rd (3G) generation mobile communication system. In addition, the next generation wireless communication systems are expected to support a higher data rate than that of existing wireless communication systems. Therefore, the next generation wireless communication systems should be able to support a variable asymmetric service that efficiently provides multimedia traffic, and to reliably support a high data rate. “Asymmetric service” refers to a service in which a forward link (or downlink) and a reverse link (or uplink) have different data rates. Since the multimedia service is generally received at a mobile station, multimedia traffic needs a higher data rate on the forward link. In addition, the asymmetry rate must be variable. Herein, the “forward link” means a link from a base station to a mobile station, while the “reverse link” means a link from the mobile station to the base station.
Typically, duplexing technologies that can be used in wireless communication systems are classified into time division duplexing (TDD) and frequency division duplexing (FDD). A brief description of these duplexing technologies will be made herein below.
Time division duplexing refers to communication technology that divides transmission/reception by time. In this communication technology, for mobile stations, time for which data can be received and transmitted over a forward link and a reverse link is uniquely determined. In this way, the mobile stations perform communication within their unique times. At this point, a base station can assign a part of or all of the available time slots to a mobile station in communication. Therefore, time division duplexing is suitable to providing an asymmetric service by differentiating a time slot assigned to a forward link from a time slot assigned to a reverse link, both of which are set up between a base station and a particular mobile station. However, in time division duplexing, an increase in cell coverage causes round-trip delay, thereby increasing a guard time and undesirably decreasing transmission efficiency during transmission/reception. Therefore, time division duplexing. is not suitable for a cell having wide cell coverage, such as a macrocell. Moreover, in time division duplexing, since cells have different asymmetry rates in a cell environment, co-channel interference between mobile stations is undesirably increased.
Frequency division duplexing refers to communication technology that divides transmission/reception by frequency. In this technology, frequencies at which data can be received and transmitted over a forward link and a reverse link between a base station and a mobile station are individually set. In addition, communication between the mobile station and the base station is performed all the time using the set frequencies. Therefore, frequency division duplexing has no round-trip delay problem and is suitable to a macrocell. By virtue of wide coverage of the macrocell, frequency division duplexing can provide a service appropriate to a mobile station that moves fast from place to place. However, since a frequency band is symmetrically and fixedly assigned, frequency division duplexing has a limitation in providing a variable asymmetric service.
Since the next generation wireless communication service is required to support a high data rate for a mobile station that moves at high speed, there is a demand for a system that makes the best use of the advantages of time division duplexing and frequency division duplexing.
However, building a TDD cellular network up to a position where density of mobile stations is very low, with only TDD, which is suitable to a microcell, is disadvantageous in terms of economical efficiency.